Motion picture film typically contains signal-dependent noise, often referred to as film grain, resulting from the process of exposure and development of the photographic film. Such noise yields a characteristic quasi-random pattern or texture, caused by the physical granularity of the photographic emulsion. Alternatively, signal-dependent noise can occur as result of subsequent editing of the images. The grain pattern can be simulated for video compression purposes.
The ITU-T H.264|MPEG-4 AVC video compression standard has accepted in its Fidelity Range Extensions Amendment the inclusion of a film grain SEI (Supplemental Enhancement Information) message. The film grain SEI message conveys a series of parameters allowing film grain simulation at the receiver. For the ITU-T H.264|MPEG-4 AVC compression standard, parameters in the SEI message can be specified according to two different models: the auto-regressive model and the frequency-filtering model. Both models allow characterizing the film grain pattern (size and shape), intensity and color correlation through different sets of parameters for different intensity levels. In particular, the frequency-filtering model characterizes the film grain pattern by specifying a set of cut frequencies that define a 2D band-pass filter in the frequency domain. Note that ITU-T H.264|MPEG-4 AVC only standardizes the syntax necessary to transmit the cut frequencies but does not provide a method for computing them for a video sequence with film grain.
Thus, there exists a need for a technique allowing the automatic modeling of the film grain pattern in the frequency domain as specified by the frequency-filtering model in ITU-T H.264|MPEG-4 AVC compression standard. Results for this technique could be used either for automatic film grain modeling applications or as the initialization step for a film grain assisted-modeling process.